Characteristics of physiological data during asymmetric gait of healthy subjects using a two-belt treadmill

1. Introduction

Many people suffer from paralysis due to various reasons such as stroke or spinal cord injury. Patients with hemiplegia require many types of repetitive rehabilitation training to perform daily activities. These therapies can be physically demanding on the therapist. According to Bork et al. [1], physical therapists often have muscular skeletal diseases. Especially gait rehabilitation, which is nearly the last step of rehabilitation, requires considerable labor. To reduce the labors of the physical therapist, many cutting-edge technologies have attempted to use a gait rehabilitation training system. Many gait rehabilitation systems have been developed for paralysis patients using robots. These have numerous advantages such as cost effectiveness and motivating patients [2, 3, 4]. The robot gait rehabilitation systems must help support patients’ body weight to help with balance and prevent falls as well as strengthen muscles for walking [5]. Robot gait rehabilitation systems can be roughly divided into four sections for different symptoms: treadmill base, foot plate base, stationery robotic base, and mobile robotic base [6]. Among other applications, mobile robotic base gait rehabilitation systems are used for both the nearly last step of gait rehabilitation and for daily life assistance by inducing natural walking [7, 8, 9]. To function independently in everyday life, safety is the most important issue. For safety reasons, healthy people without gait disability are often used for evaluating systems before allowing patients to use them. However, these experiments are insufficient because there are many physical differences between healthy people and paralysis patients. It is important to reduce this testing gap for developing and growing systems.

Wentink et al. [10] attempted to induce hemiplegic gait in healthy people by restraint motion of joint angle. Choi and Park [11] used heavy clothes to imitate abnormal gait. There is a time difference between the paralyzed and non-paralyzed legs in the stance and swing phases of hemiplegic gait, which is rarely observed in healthy subjects. In addition, measurements of the EMG on skin like surface is difficult because the subjects wore some clothes for restraints. To develop a two-belt treadmill for gait rehabilitation protocol in hemiplegic patients, studies on the biomechanical analysis of asymmetrical gait in healthy adults are insufficient.

This study aimed to analyze the characteristics of lower extremity muscle and foot pressure in healthy adults for unbalanced walking with left and right speed difference using a two-belt treadmill. We assumed that an asymmetric gait can be imitated by a difference in the left and right side velocities of two-belt treadmill.

2. Experimental method

3. Results

Perry [12] and Hesse et al. [13] reported that hemiplegic patients have shorter stance phase and long swing phase on the sides of legs in paralysis. However, in non-paralysis, there are longer stance phase and short swing phase on the sides of legs to compensate the abnormal walking. Adjusting the velocity makes it possible to imitate the asymmetrical gait characteristics in a healthy subject. Because of the velocity, the faster side of the leg has a short stance phase and a long swing phase, which is similar to the gait characteristics in paralysis. However, there are longer stance phase and shorter swing phase in the slower side than the faster side. This is exact opposite to that observed in the gait of hemiplegic patients, who spend a longer time on the paralyzed leg [14, 15].

The foot pressure was concentrated more on the rearfoot than the forefoot in the slower side. This means that a pre-swing phase rarely occurs in the slower side of the leg. This is similar to the non-paralysis side of legs in hemiplegic patients [14, 15]. On the contrary, the faster side of foot pressure indicated exactly opposite results to the slower side. The concentration on the rearfoot on the faster side is caused by the toe-off phase; however, there is a difference in the hemiplegic patients’ gait patterns on the paralysis side [14, 15]. Because of the patients’ asymmetric patterns, the toe-off phase occurs. The asymmetry between the anterior and posterior foot pressures is large when the velocity gap is large. In other words, we expect that the degree of paralysis could be set by changing the velocity gap between two belts. According to the bodyweight support, the pressure on the lateral section of the foot statically decreased in both faster and slower sides. The decrease of pressure on the medial side of the foot pressure on slower side was also affected. The pressures on the anterior and posterior sides of the foot significantly decreased on both sides of the foot with bodyweight support, except on the anterior section of the faster side leg. The dissymmetry existed even with bodyweight support.

The EMG results show that the RF and Lat.Gas muscles were more activated on the faster side than the slower side. This is caused by the toe-off in pre-swing phase [15, 16, 17]. However, the TA and BF muscles were more activated on the slower side than the faster side because the slower side required a longer stance phase.

5. Conclusion

In this study we attempted to imitate asymmetrical gait patterns using two-belt type treadmill to aid in developing mobile a gait rehabilitation system with healthy subjects before using the system with patients.

We hypothesized that hemiplegic gait can be imitated using a speed difference between the left and right sides and verified the hypothesis through the experiments. We observed that the gait pattern of the slower side was similar to that of the non-paralyzed leg, and the gait pattern of the faster side to the paralyzed leg in hemiplegic patients. However, the gait pattern of the faster side indicated differences from the patients, because healthy people employ toe-off in pre-swing phase. In addition, we found that that the greater the speed difference, the greater the asymmetry in the foot and muscles action. Therefore, we can control the degree of paralysis by controlling this difference.

We also performed experiments with bodyweight support, which is a basic function of a gait rehabilitation system. Despite the bodyweight support, asymmetry was still present in both pressure concentration and muscles.

Despite its limitations, the proposed method improves the process of verifying novel gait rehabilitation systems before being used by hemiplegic patients. In the future, we will apply this method to a mobile robotic system, and we expect that we can set other asymmetrical gait patterns combined with velocity control and bodyweight support rate between the left and right sides. The quantitative results of this study can be used to develop a training protocol for two-belt treadmills with differently controlled speeds in the left and right sides for gait rehabilitation for hemiplegic patients.